he says the u.s. must maintain its own strength to create stability around the world. >> it is our responsibility and the responsibility of the president to use america's greatest power to shape history. >> reporter: both candidates have talked about relations with china but often in economic terms. neither has explained enough how he would deal with beijing diplomatically. china is now the world's second largest economy. it's also strengthening its military power and it's growing more assertive in territorial disputes. professor zhao quansheng is an expert on asian policy at american university in washington, d.c. he says both obama and romney would, if elected, continue the u.s. policy of engagement in the region. >> asia-pacific is a natural choice for the priority of u.s. foreign policy given the very size of economy, and this is the most dynamic region in the world. think about -- i mean, u.s., china, japan. number one, number two, number three economies, all in asia pacific. >> reporter: zhao sa